Abstract
The inflammatory microenvironment in the retina plays a vital role in the pathogenesis and progression of retinitis pigmentosa (RP). Microglial inflammatory cytokines production leads to gliosis and apoptosis of retinal neurons, and ultimately, visual loss. Cell-based therapies using grafted olfactory ensheathing cells (OECs) have demonstrated modulation of degenerative microenvironments in the central nervous system (CNS), in a number of animal models. However, mechanisms by which grafted OECs can reduce degeneration in the retina are not well understood. In the present study, we set up an in vitro OEC/BV2 microglia co-culture system, and an in vivo royal college of surgeons (RCS) rat model, used cell transplantation, immunohistochemistry, RT-PCR, western blot to explore the mechanisms by which OECs affect expression of pro- or anti-inflammatory cytokines and polarization of M(IL-6) and M(Arg1) type microglial activation in the retina. We found that compared with the LPS (Lipopolysaccharide) and olfactory nerve fibroblast (ONF), the OEC and BV2 co-culture group modulate microglial cytokines releasing toward the anti-inflammation, and away from the pro-inflammation, which was followed by higher IL-4 and IL-10 and lower TNF-a and IL-6 in their expression levels. In vivo, the transplantation group significantly reduced activated resident microglia/infiltrated macrophage, and expression of pro-inflammatory cytokines in RCS rats retina, increased anti-inflammatory cytokines in transplantation area. Additionally, we found that OECs expressed SOCS3 and down-regulated the JAK2/STAT3 (Janus Kinase 2/Signal Transducer and Activator of Transcription 3) pathway. Thirdly, OEC transplantation reduced Caspase-3 expression, protected inner retinal neurons and photoreceptors and therefore, delayed the visual function degeneration. In conclusion, our data suggest that OECs delay retinal degeneration in RP, at least in part through immunomodulation of microglia via the JAK/STAT pathway.
Highlights
Retinitis pigmentosa (RP) is a heterogeneous group of inherited retinal degenerative diseases, which lead to photoreceptor cell apoptosis and severe vision loss
We have shown how olfactory ensheathing cells (OECs) can affect LPS-induced microglial activation profiles in vitro, how OEC transplantation in vivo can moderate the inflammatory microenvironment, protect photoreceptor and improve visual function, in chronic retinal degeneration animal model
In vitro classically activated immune cells up-regulated JAK2/STAT3 experiments showed that OECs exert immunomodulatory effects pathway and produce persistent pro-inflammatory factors, but through a change of expression level of inflammatory factors in LPS-induced microglia activation: away from M(IL-6)-type (TNF-α, IL-6, MCP-1 and ICAM-1), toward M(Arg1)-type (Arg1, IL-4, IL-13), via a mechanism that is dependent on the JAK2/STAT3 pathway
Summary
Retinitis pigmentosa (RP) is a heterogeneous group of inherited retinal degenerative diseases, which lead to photoreceptor cell apoptosis and severe vision loss. Photoreceptor degeneration starts from microglial activation, macrophage infiltration, and accumulation of immunoglobulins and complement, which result in sustained inflammation, macroglia proliferation and progressive apoptosis of retinal neurons (Athanasiou et al, 2018; Ben et al, 2019). In royal college of surgeons (RCS) rats with Mertk gene mutation of retinal pigmented epithelium (RPE), microglia become activated, and infiltrate into the outer nuclear layer (ONL), to assist with phagocytosis of photoreceptor debris (Zou et al, 2019). Bloodretinal barrier (BRB) disruption results in the recruitment of blood-borne macrophages. This is an important step in activating the immune cells and releasing pro-inflammatory cytokines, which amplify the disease process, and leading to photoreceptor apoptosis (Kyger et al, 2013). Studies have already shown that blood-derived immune cells are an important component of the disease-associated microenvironment, and they are considered to be critical mediators of neurodegenerative disease progression, in CNS and in retina (Xu et al, 2009; Sevenich, 2018)
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